A man about to stand trial for a third time on charges of having sex with his girlfriend's teenage son and daughter, who called him father, unexpectedly pleaded guilty yesterday.

The jobless man, 43, stood trial for the first time in 2007 on nine charges, but the jury acquitted him of two of them and was hung on the other seven. In another trial that year on the seven charges, he was convicted on all counts and jailed for 18 years.

In May, the Court of Appeal ruled that the judge at the second trial had failed to properly direct the jury. It quashed the convictions, allowed the man's appeal, and ordered a retrial. The retrial was due to start yesterday at the Court of First Instance and was scheduled to last nine days.

The man pleaded guilty before Madam Justice Maggie Poon Man-kay to two counts of non-consensual buggery and three of having unlawful sexual intercourse with a child.

The man had sexual intercourse and anal sex with the children at his flat in Tsz Wan Shan. The boy was 13 and the girl aged 13 to 15 when the incidents took place.

Senior prosecutor Peggy Lo Suk-ling said the children's mother had met the man in 1991 and became his girlfriend. When she and her husband separated, she moved in with him, bringing the children along. 'Both of the victims called the defendant father,' Lo said.

She broke up with him in 2000 and moved out, taking the children, Lo said. However, they later rekindled their relationship.

The events to which the man admitted yesterday occurred after the children had moved away. He molested the boy after telephoning him to tell him to go to his flat to retrieve computer parts. He had sex with the girl on separate occasions at his home. He did not use a condom when he molested the boy and on one occasion with the girl.